The invention relates to a liquid indicator, particularly a precipitation indicator, such as a rain indicator.
Liquid indicators can e.g. be used for determining the precipitation situation in the form of stationary rain indicators in the domestic and garden sector, so as to control an automatic watering system. A device of this type must e.g. be in a position to emit one or more precipitation signals in the case of rain, long-lasting, dense fog or other wetting precipitations and on whose reception the watering system can be switched off, so as to prevent overwatering of the monitored area and save water. One or more dry signals are to be emitted if precipitation adequate for the desired or necessary wetting action does not fall, so that the watering system can assume responsibility for providing the necessary wetness.
The problem of the invention is to provide a liquid indicator more particularly usable as a precipitation indicator. The device must in particular be in a position to make a reliable distinction between precipitation situations and dry situations.
This problem is solved by a liquid indicator having the features of claim 1.
The liquid indicator usable as a rain indicator and as a result of this preferred application also called a precipitation indicator has at least one light source and at least one light guidance body or light guide, which is made from a material transparent to the light of the light source. The light guide has at least one surface portion, which is intended for contact with the liquid, particularly the liquid precipitation and which is so positioned relative to the light source that the light of the latter is totally reflectable on the surface portion if total reflection conditions exist on said surface portion. There is also at least one light detector, which can be brought into light-conducting connection with the light source by means of the surface portion.
Thus, an optical liquid or precipitation sensor is created, in which in the case of liquid, particularly precipitation, modifies the light conditions between the light source and the light detector to a significant extent. For as long as the surface portion is substantially dry, because there is e.g. little or no adequate precipitation, on the surface portion the optically dense material of the e.g. glass or visible light-transparent plastic light guide with a typical refractive index of well above 1, e.g. approximately 1.5 and the gaseous ambient atmosphere with a typical refractive index of approximately 1 are adjacent to one another. If the surface portion with respect to the light falling from the light guide side coming from the light source with respect to the average incidence direction relative to the normal to the reflecting surface is at an incidence angle greater than the material-specific critical angle of the total reflection, then the light is totally reflected on the surface portion and at this point cannot leave the light guide and is instead toally reflected into its interior. With such a dry situation one or more dry signals associated with the dry state are emitted. However, if the surface portion, particularly due to precipitation, is in contact with water and is more particularly wetted by the latter, due to the higher refractive index of water compared with air of typically approximately 1.3, the reflection conditions at the surface portion change in such a way that there is no total reflection and instead light passes out of the light guide at the surface portion, i.e. is coupled out of the same. This wetting situation referred to as the precipitation situation leads to the emission of one or more liquid or precipitation signals. Following adequate drying of the surface portion, once again total reflection conditions occur and a dry signal can be emitted. Further developments are explained hereinafter using the example of a precipitation indicator and the term xe2x80x9cprecipitationxe2x80x9d can optionally also stand for other liquids.
For the detection of the precipitation on the surface portion it is possible to use the light intensity transmitted by the latter and also the totally reflected intensity, either in alternative or combined form. In a preferred embodiment the light detector is so positioned with respect to the surface portion, that substantially only the light source light totally reflected by the surface portion is detectable. A direct light conduction between the source and the detector is appropriately prevented. The exclusive use of the reflected intensity for precipitation detection is inter alia advantageous because the light detector can then e.g. be positioned within the light guide and/or the solid side of the surface portion, which permits a compact construction and also facilitates the protection of the light detector against moisture and damage.
Particular preference is given to embodiments in which in the light path between the light source and light detector there are several and in particular two surface portions at an angle to one another, which are so positioned relative to the light source and one another, that the light of the light source can be totally reflected by them to the light detector. As a result of the thus possible at least double deflection between the light transmitter or source and light receiver or detector, there is a significant rise in the distinction reliability between the dry state and the precipitation state, because there is only an adequate light intensity at the light detector if there are total reflection conditions, due to dryness, on all the totally reflecting surface portions in the light path.
Particular preference is given to embodiments in which at least two surface portions are positioned in such a way that the light source light, in the case of total reflection is deflected by more than 90xc2x0, particularly substantially by 180xc2x0. This permits a compact construction, in which the light source and light detector can e.g. be closely juxtaposed on one side of the light guide, whereas the surface portions to be wetted are located in the area of the opposite side. The light guide can e.g. have a circular conical segmental part with an aperture angle of approximately 90xc2x0 on which are arranged in diametrically facing manner curved, totally reflecting surface portions, which can exert a certain light focussing action. It is also possible for the light guide to have at least two planar surface portions at an angle of 90xc2x0 to one another and e.g. constructed in the form of a roof prism.
It is possible to use any suitable light source or combination of light sources and any suitable light detector responding to the light source light. Particularly cost-effective, reliably functioning and energy consumption-favourable embodiments are characterized in that the light source has at least one and preferably precisely one light emitting diode and/or that the light detector has at least one and preferably only one photodiode. An energy saving effect can be obtained if there is a device for the continuous operation of the light source, particularly for pulsed operation and optionally the pulse spacing can be adjustable. The time interval between successive and optionally very short light emissions can be in the second or minute range, e.g. approximately 10 or 30 or 60 seconds or more. Particularly consumption-favourable embodiments can advantageously operate in mains-independent manner and can e.g. be supplied with electric power by batteries, accumulators and/or photovoltaic elements. However, a mains-dependent supply is alternatively or additionally possible.
In preferred embodiments there is at least one precipitation reservoir for collecting precipitation and then a precipitation reservoir is preferably adjacent to a surface portion. As a result the response reliability of the indicator can be increased and erroneous indications are largely avoided, because a signal change from dry to precipitation will, in the case of a corresponding design, only occur with an adequately filled precipitation reservoir, so that possibly unproductive, short showers are not interpreted as a precipitation situation and cannot e.g. lead to the disconnection of a controlled watering system. It is preferably for the precipitation reservoir to be constructed as a capillary reservoir, in which capillary forces significantly bring about and/or promote a filling of the reservoir and/or a keeping of liquid in the reservoir. The reservoir can be so designed that it only fills in the case of precipitation with a specific intensity and/or that following the fading away of the precipitation there is still a certain time lag until the reservoir content evaporates, so that only significant, relatively long-phase changes between precipitation and dryness lead to signal changes.
In preferred embodiments there is at least one gap formed between the surface portion and an opposing surface, in which precipitation, optionally assisted by capillary forces, collects and can be retained for a certain time. For example by suitable colouring and/or surface design, e.g. roughening or stepping, the opposing surface can be constructed as an absorption surface for the light source light, so that light intensity entering the liquid-filled gap when total reflection ends is essentially absorbed by the opposing surface and cannot pass as stray light to the light detector.
Embodiments with an adjustable response threshold are particularly advantageous, i.e. when the precipitation intensity at which the sensor is to respond can be fixed by the user. In embodiments with a precipitation reservoir this can be particularly easily implemented in that said reservoir has an adjustable capacity and preferably the shape and/or size of the gap adjacent to the surface portion can be adjusted.
Further measures for improving the precipitation indicator, particularly its response reliability, are explained hereinafter in conjunction with preferred embodiments. It is in particular possible to associate with the indicator collecting means for collecting precipitation, which are connected by means of a precipitation supply device in liquid-conducting manner to the surface portion, particularly the precipitation reservoir. This makes it possible to provide a relatively large collecting surface for the precipitation, whilst the surface portion area necessary for precipitation detection can be kept very small. A corresponding funnel action can be obtained by suitable design elements on a casing of the precipitation indicator, e.g. by suitable water guidance channels on a casing outside, the water guidance channels comprising vertical grooving on an upper portion of a casing and/or collecting guides converging in funnel-shaped manner on the casing circumference and inclined to the vertical.
Retention means, explained in greater detail in conjunction with the embodiments, can be provided for retaining the precipitation on the surface portion, particularly in the precipitation reservoir, which in particular makes it possible to set a suitable time lag between the ending of precipitation and the emission of a dry signal. For this purpose e.g. web-like elements located in a gap adjacent to the surface portion can form additional wetting surfaces for the precipitation, which suitably delay the flowing away or evaporation of the reservoir content. The elements can be simultaneously used as spacing elements for adjusting and maintaining a suitable gap geometry.
Preferred embodiments of inventively operating precipitation indicators are characterized by a modular construction with several, detachably interconnectable parts. In particular, there is a preferably cartridge-shaped, particularly moisture-tight sealable indicator upper part, which can be inserted into a preferably cylindrical, top-open basic casing with a larger diameter and this takes place portionwise in such a way that between an outside of the indicator upper part and a basic casing wall is formed at least one entry gap, which can e.g. be a circumferential annular clearance or can be formed by several annular segments. The outside of the indicator upper part projecting over the lower part can be used for large-area precipitation collection and the collected precipitate can pass through the entry gap into the otherwise substantially outwardly protected interior of the basic casing.
The light source, a control electronics for the light source, the light detector, an evaluation electronics for the light detector and the light guide can be so arranged on and/or in a casing part of the indicator, particularly its upper part, that the surface portion forms part of the outer surface of said part. In particular the light guide can form a lower termination of the indicator upper part and preferably at least one surface portion is arranged substantially in an extension of the outer surface of the indicator upper part, so that liquid running on the exterior of said upper part flows to the surface portion.
Such an indicator upper part, which preferably also has a watertight sealable reception space for a power supply for the control and evaluation electronics, can be used not only in the case of precipitation indicators according to the invention, but e.g. also as autarchically operating liquid indicators in a container, pond, etc. In such cases there is no need for measures for the supply, maintenance and/or removal of liquid and/or a liquid reservoir. A liquid signal can be emitted if the surface of a liquid to be monitored has risen to the vicinity of or above the surface portion.
For the creation of a precipitation indicator the indicator upper part and basic casing can be detachably interconnected preferably without tools and preferably the upper part can be fixed in the basic casing and/or screwed to the basic casing, e.g. by means of a manually operable cap nut. The basic casing can have a counterbody with the gap opposing surface, so that by adjusting the position of the indicator upper part in the basic casing, it is possible to adjust the shape and/or size of the gap serving as a precipitation reservoir.
The indicator can be fixed in a stable, stationary manner in the vicinity of the area to be monitored, e.g. by means of a screw-down mandrel or the like, feet or other fastening means. The signals for indicating the dry state or precipitation state can be emitted to the outside by means of cables or without wires, e.g. by means of an integrated infrared transmitter, for the purpose of the further processing of said signals.
These and further features can be gathered from the claims, description and drawings and the individual features, either singly or in the form of sub-combinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous constructions.